A productive day full of hard work for Team SPAW. Jenna and Ashley finished up their hydrometer measurements and Natasha and Char worked on creating maps of the reservation based on their interviews with tribal members and elders. Rik helped me with making maps of the sampling transects from GPS waypoints, and all of us have been meeting with Tony to discuss edits on our papers. We’ve also been itching mosquito bites we got yesterday at the pond, and combing tangles out of our hair from the drive around the Bison Range. Looking forward to the video conference tomorrow – can’t wait to show our pictures of Yellowstone, etc and to hear about what everyone else has been up to.
Today team Zaaga’igan made lots of progress! We worked on data, bibliographies, and our papers today. Some of us have at least twelve graphs. To finish off a hard day of work,we went to Gordies for dinner and the warming house for desert. Overall it was an extremely productive day.
Tuesday we had the opportunity to go the the Bison Range and teach a group of student from all over south east Asia about clean water and macro invertebrates. We had a great time collecting the critters and even found some cray fish. We had lunch with them and answered many of their questions not just about water but life of college students in America.
I am researching how wind flows behind wind turbines by analyzing experimental and numerical data. The experimental data has been collected around the turbine that is pictured below; and the numerical model is based on this turbine.
I’m specifically analyzing the structure and evolution of the vortices that are created at the blade tips. Turbines’ blades rotate because the aerodynamic shape of the blades guides incoming wind into creating a pressure difference that, in turn, drives the blades. Objects feel forced to move to lower pressures. Both the blades and the wind are forced into the lower pressure. Some wind wraps around the blades in order to get from the low pressure area. A vortex forms where the wind curls because the low pressure applies a centripetal force – like how a hurricane is a vortex where wind wraps around the hurricane’s low-pressure eye. Vorticity quantifies how much the fluid rotates around a region. In math terms, the vorticity is the curl of the wind velocity. Strong vortices are created at the blade tips; because here the wind can radially bypass the blade, which provides an easier path in the pursuit of lower pressure. This vortex is then pushed downstream by the wind; away from the blades’ low pressure region, the wind continues to curl due to a law of angular momentum conservation. The tip vortices are major sources of turbulence that damage downstream turbines. Consequentially, tip vortex research can lead to improvements in the longevity of turbines in wind farms.
I have made most of my current research progress by using a colleague’s numerical simulation that estimates wind velocity around a wind turbine. I am examining how tip vortices change across time and space. One specific investigation concerns the merging of two adjacent vortices. Since corotational vortices attract each other, the tip vortices sometimes merge together. To quantify this process, I am measuring the distances between adjacent vortices and the areas of those vortices. I hypothesize that by graphing the ratio of their distance to their area as they move downstream, I will find distinct phases in the merging process. I believe that when this ratio of distance to area decreases below a certain level, they will accelerate towards each other much more quickly.
A two dimensional slice of a numerical simulation is depicted below. The color shows the vorticity magnitude; the downstream direction is right, and the ground is located about 100 m below the x axis. The top of the turbine blades would be located on the lower left; here you can see distinct circular tip vortices in red. Farther downstream, the vortices appear to interact, as the vorticity in between the vortices is higher than it is upstream.
The image below depicts how these vortices merge into a vortex sheet. This vortex sheet does not always develop, for it depends on the amount of incoming turbulence and on the ratio of the wind speed to the turbine’s rotational velocity. The color scheme has been changed since the last image to emphasize the merging process.
While I work in Minneapolis, MN, I live in St. Paul. I am staying with 5 Macalester College students. The rent is great: $200/month for the best room in the house (it has great big windows). This is my first time living in a college house, and I like it; for there are usually people around to talk to. I enjoy the camaraderie of the house. The Twin Cities have been very nice. Minneapolis’s culture is a lot like Portland’s. Everyday, I take 6 miles of fabulous biking trails to work. This is a tiring, yet rewarding, ride. When it rains, I use the cities’ good public transportation system. I have gone to fun, free events, including a museum, a jazz festival, a hip hop/spoken word festival, a bike race, a play, fireworks, and a swimming lake. I have been thinking about living here in the future, but the cold winters and the mosquito-infested summers might keep me away. I have, however, successfully fought off the mosquitoes; and I am thoroughly enjoying my time.
It has been a while since I’ve posted, but here’s a quick update from the CivE building! We are all furiously working on analyzing our data. No one has used the specific code that we are using before in this research group, so we are slowly finding our way to the end together.
Last weekend, we also made a trip to First Avenue for a concert and to the Como Park Zoo and Conservatory!
Another task driven day in the lab. Jesse and I finished our diatom counts and put them into a spread sheet. Emilia made some more oil immersion slides to use for their own diatom count tomorrow. Then in the evening we had an AMAZING dinner of Corn soup and fry bread made by Ma’Ko’Quah on her birthday and a pretty damn good cake made by me. Overall it was a nice day and an even better evening.
First picture is of a microscope view. The large oblong pieces are diatoms.
Second Picture is Emilia grossly immersed in the drying process of oil immersion slides.